A polycarbonate resin is widely used in many fields as engineering plastics utilizing its excellent heat resistance, impact resistance, transparency and dimensional stability. A method of introducing phosgene under mixing an alkali aqueous solution of an aromatic dihydroxy compound and a halogen organic solvent to thereby reacting the aromatic dihydroxy compound and phosgene at the interface (interfacial method) and an ester exchange method of reacting an aromatic dihydroxy compound and a carbonic diester under a molten state (melt process) are known as an industrial production method of this polycarbonate resin.
Where a polycarbonate resin is produced by the latter ester exchange method (melt process), in general a carbonic diester and an aromatic dihydroxy compound as raw materials are dissolved, an ester exchange catalyst is added to this, and stirring is carried out under heating in a polymerization tank under reduced pressure. Polycondensation reaction by an ester exchange reaction proceeds while distilling by-products such as aromatic monohydroxy compounds and/or aliphatic monohydroxy compounds, and a polycarbonate resin is produced (see Patent Document 1).
By the way, the melt process may give rise to the problems such that white foreign matters are incorporated into a polycarbonate resin and a pipe line clogs, during continuous operation for a long period of time, and for those problems, various countermeasures are reported. For example, there are the following methods; a method of preventing solidification of distilled components by providing a reflux piping having a predetermined gradient in an apparatus of distilling phenol and diphenyl carbonate by by-produced during a polycondensation reaction, under reduced pressure (see Patent Document 2), a method of washing a polymerization tank, a transfer piping and the like with a monohydroxy compound or the like within 24 hours after completion of continuous operation (see Patent Document 3), and a method of controlling surface temperature of a polymerization tank with which a low molecular weight polycarbonate formed in the course of polycondensation reaction contacts, a transfer piping of a molten reactant, stirring blades and the like, thereby suppressing crystallization (see Patent Document 4).
Patent Document 1: JP-A-2003-192782 (see FIG. 1)
Patent Document 2: JP-A-2005-145841
Patent Document 3: JP-A-2005-042014
Patent Document 4: JP-A-2000-198839